1. Field of the Invention
The present invention relates to a magnetic field measurement optimization apparatus using a charged particle beam and, more particularly, to a magnetic field measuring apparatus capable of measuring the distribution of magnetic field intensity in the vicinity of a sample.
2. Description of the Related Art
The recording density of magnetic recording apparatus, such as magnetic disk memories, magnetic tape recorders and VTRs, has been increased remarkably in recent years, and the further improvement in performance of magnetic heads to be incorporated into such magnetic recording apparatus has been required. The magnetic head must be capable of recording information in a narrow track having a sharp recording field intensity distribution to achieve high-density magnetic recording.
The reduction of the dimension of the magnetic head along the width of the track to establish a sharp recording field intensity distribution brought about a significant problem that leakage flux across tracks causes erroneous writing in the adjacent tracks. Thus, the development of a magnetic head that produces less leakage flux across tracks has been required. A magnetic field measuring apparatus capable of minutely measuring the distribution of magnetic field intensity in a recording magnetic field created by a magnetic head is essential to research for the development of a magnetic head suitable for high-density recording.
A known magnetic field measuring method for measuring the distribution of magnetic field intensity in a recording magnetic field created by a magnetic head passes an electron beam through the magnetic field created around the magnetic gap of the magnetic head to measure the magnetic field intensity at a position through which the electron beam is passed through the measurement of the deflection of the electron beam by the Lorentz force of the magnetic field. The magnetic field is scanned by the electron beam to determine the distribution of magnetic field intensity in the magnetic field.
Another known magnetic field measuring method measures the three-dimensional distribution of magnetic field intensity in a magnetic field. This method rotates gradually a sample that creates a magnetic field, scans the magnetic field with an electron beam with the sample at different angular positions, measures the deflection of the electron beam by an electron beam detector, and determines the magnetic field intensity at each position in the magnetic field through calculation using the variation in the detected position of the electron beam, i.e., the variation in the deflection of the electron beam. Detection signals provided by the electron beam detector are stored in a computer, and the detection signals are processed by a computerized tomography method (hereinafter referred to as "CT method") to reconstruct the three-dimensional distribution of magnetic field intensity in the magnetic field.
Results of such measurements of the three-dimensional distribution of magnetic field intensity are stated in "49th Oyo Butsuri Gakkai Gakujutsu Keen Yoko-shu", p. 559, Oct., 1988 and "IEEE Transactions on Magnetics", vol. MAG-21, No. 5, pp. 1593-1595, Sept., 1985.
For the two-dimensional measurement of the leakage flux of a magnetic head having a very narrow magnetic head gap, the magnetic field intensity must be measured at positions as near as possible to the magnetic head gap. To meet such a requirement, the scanning electron beam must be controlled so as to fall at positions as near as possible to the surface of the magnetic head gap. To control the electron beam in such a manner, the position of the incident scanning electron beam must be controlled and the the position of sample stage for holding the sample magnetic head must be adjusted in high accuracy. Also in the measurement of the three-dimensional distribution of magnetic field intensity by the CT method, the electron beam must be controlled while the sample magnetic head is turned through an angle of 180.degree. so as to fall at a position as near as possible to the surface of the magnetic head at each angular position of the magnetic head. Accordingly, the angular position of the sample magnetic head must be controlled in high accuracy and the sample stage must be controlled in high accuracy for the optimum positioning of the sample magnetic head with respect to the three dimensional directions, i.e., the X, Y and Z directions, because the final accuracy of measurement of the three-dimensional distribution of magnetic field intensity is dependent on the accuracy of sample stage control. Since the electron beam is passed through a position at a very short distance on the order of several micrometers from the surface of the sample magnetic head, the electron beam may fall on the surface of the sample magnetic head to make the measurement of the distribution of magnetic field intensity impossible if the positional relation between the electron beam and the surface of the sample magnetic head, namely, the position of the electron beam on the Z axis relative to the surface of the sample magnetic head, changes even a little bit.